4.2. Cambrian Explosion

How did life emerge on Earth? How have life and Earth co-evolved through geological time? Is life elsewhere in the universe? Take a look through the 4-billion-year history of life on Earth through the lens of the modern Tree of Life!
This course will evaluate the entire history of life on Earth within the context of our cutting-edge understanding of the Tree of Life. This includes the pioneering work of Professor Carl Woese on the University of Illinois Urbana-Champaign campus which revolutionized our understanding with a new "Tree of Life." Other themes include:
-Reconnaissance of ancient primordial life before the first cell evolved
-The entire ~4-billion-year development of single- and multi-celled life through the lens of the Tree of Life
-The influence of Earth system processes (meteor impacts, volcanoes, ice sheets) on shaping and structuring the Tree of Life
This synthesis emphasizes the universality of the emergence of life as a prelude for the search for extraterrestrial life.

SZ

AB

May 20, 2020

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Really fascinating videos and engaging lecturers. I learned a lot!

從本節課中

Week 4 - Paleozoic Life After the Advent of Skeletons

This week, you'll learn more about the Cambrian Explosion, which led to the development of external hard skeleton components at 542 million years before present. The initial successes of the invertebrates were shortly followed by the appearance of vertebrates with internal skeletons. Life then utilized these newfound evolutionary capabilities, beginning distinct cycles of radiation, diversification, and extinction, which define the three great Eukarya faunas of the Phanerozoic.

教學方

Bruce W. Fouke, Ph.D.

腳本

[SOUND] [MUSIC] Evolutionary biology has played out through geological time in producing brand new organisms that appear on planet Earth. They do very well and expand, and we call that radiate. And then, through geological time, eventually these organisms fall away, they don't do well, they go extinct, they stop existing. And that extinction process is the cap on this origination, radiation, and extinction cycle that goes on. Now, the great origination event when it comes to the Metazoans is what we call the Cambrian Explosion. And that Cambrian Explosion was a series of organisms that were Metazoans, multiple celled. And they grew something really important that hadn't been on the scene before in terms of evolutionary biology, and that was a skeleton. And the skeletons that were produced by these Metazoans were external, they were outside of the body. So we call those invertebrates. The other corollary to this of course are the Metazoans that grow skeletons inside their bodies, and we call those vertebrates. And we're going to save the vertebrates for a little bit later in looking at their evolution. But the first organisms to radiate, originate, and expand were the invertebrates. So the Cambrian Explosion is marked by this remarkable event of the sea floor suddenly being populated by these relatively large, centimeters plus in size, organisms that grew these exoskeletons. And the skeletons permit the organisms to do a lot of things they can't do without skeletons. And one of the things they do is they allow to have greater body size. It provides physical support within the water and from gravity. It also has advantages in terms of protection from predation. If you're just soft and squishy, and you're on the sea floor, something's going to come along and get you. But if you have some kind of a fortress around you called an exoskeleton, then you can ward off your predators sometimes more easily. The problem is that, when predators face exoskeletons, the predators have this bad habit of evolving themselves to have, apparatus like jaws and teeth that can crush the skeleton, and still devour you. But that's the predator prey kind of interaction that we see through time. Now another thing that came on board with this Cambrian Explosion event was that we know the Earth was oxygenated at about 2.5 billion, but that oxygen level continued to rise. And so by the time we got to the 542 million year benchmark of the Cambrian Explosion, there was much more oxygen. And oxygen is what allows organisms to very efficiently metabolize, and therefore they can drive and develop larger body size, larger mass, and again, this capability of having skeletons. One more aspect of this is that this is all post dating the 0.6 billion year old snowball Earth when the entire Earth was covered in ice. And when that ice sheet retreated, actually went all the way from total ice coverage to no ice at all and then fluctuated back and forth a bit, that series of events opened up eco-space. And it removes some organisms that were there previously and allowed other ones to proliferate. [MUSIC]